Number of permutations that are 2 "block reversals" away from 12...n.

Terms

a(0) =2a(1) =15a(2) =52a(3) =129a(4) =266a(5) =487a(6) =820a(7) =1297a(8) =1954a(9) =2831a(10) =3972a(11) =5425a(12) =7242a(13) =9479a(14) =12196a(15) =15457a(16) =19330a(17) =23887a(18) =29204a(19) =35361a(20) =42442a(21) =50535a(22) =59732a(23) =70129a(24) =81826a(25) =94927a(26) =109540a(27) =125777a(28) =143754a(29) =163591